So! I being the fool that I am did not talk overly much with the person that turns out to have made the undead swarm cyseal. This in turn didn't update the quest about finding who the madman was.
I was wondering, not being able to talk to someone that's now dead is there a way of making that quest progress? And if not, is it important to finish said quest to go on with the game or can you simply not care, go through a magical rainbow door and enter the next area and continue on?